FAST FACTS

Slower heart rate, which is usually not dangerous, can be a side effect of medication.

Your heart relies on electrical impulses to keep it beating at a steady pace. Problems with this electrical system can cause abnormal heart rhythms, or arrhythmias. The defective impulses may cause the heart to beat too slowly or too fast, or to beat in a disorganized and chaotic manner. Some of these different types of arrhythmias can be incredibly dangerous if not properly treated, while others may be annoying but are not life-threatening.

1. Atrial Fibrillation

The most common type of arrhythmia, atrial fibrillation, affects about 2.7 million people in the United States, according to the American Heart Association. Atrial fibrillation occurs when the heart's upper chambers (the atria) begin to beat rapidly and irregularly. The condition itself isn't life-threatening, but it increases the risk for stroke by allowing blood to pool and clot in the atria — increasing risk fivefold, says Hugh Calkins, MD, an electrophysiologist and director of the Cardiac Arrhythmia Service at Johns Hopkins Medicine in Baltimore.

Atrial fibrillation risk is lower before age 50 but then steadily increases with age. Blood thinners and medication to steady the heart rate and rhythm are mainstays of treatment. In some cases, a special procedure called an ablation, which purposely scars the defective part of the heart to prevent it from passing on unwanted signals, may be recommended.

2. Tachycardia

Tachycardia occurs when your heart suddenly starts beating very fast. If it happens as a result of exercise, excitement, or fever, it's usually not a cause for concern and doesn't need treatment. But one type of arrhythmia called paroxysmal supraventricular tachycardia (PSVT) is more dangerous. It creates extra heartbeats because electrical signals that move from the heart's upper chambers to its lower chambers tend to loop back around to the upper chambers. This condition can cause sudden cardiac arrest if it affects the heart’s lower chambers, but it's curable through ablation. Tachycardia is most common in children and young people, and is more common in women than men.

3. Ventricular Fibrillation

Ventricular fibrillation is the most deadly type of arrhythmia. It occurs when the lower chambers of the heart (the ventricles) begin to quiver instead of pumping normally. Because these chambers handle most of the heavy lifting for the circulatory system, ventricular fibrillation causes blood flow to very nearly cease. "If it's not shocked in a timely fashion — and we're talking minutes — then the patient will die," says Gordon Tomaselli, MD, professor of medicine and chief of cardiology at Johns Hopkins Medicine in Baltimore.

Ventricular fibrillation usually happens in people with some sort of underlying heart condition. Those at risk can be treated with medication or an implanted defibrillator that will shock the heart if it stops beating.

4. Premature Beats

Most irregular heart rhythms involve extra or skipped beats. These types of arrhythmias are harmless and usually don't cause symptoms. People who do feel symptoms report fluttering in the chest or a feeling that their heart has skipped. Premature beats can occur in anyone, most often happen naturally, and don't require treatment. But they also can happen as a result of heart disease, stress, overexercising, or too much caffeine or nicotine. In those instances, you should talk with a cardiologist about your heart and any needed lifestyle changes.

5. Bradycardia

Bradycardia is a type of arrhythmia that, for many people, is no big deal. It means your heart rate is slower than normal — fewer than 60 beats a minute for adults. Young people and others who are very physically fit may experience bradycardia because they're in good shape, and for them it isn't dangerous and doesn't cause symptoms. But people can also have bradycardia if they've had a heart attack or if an underactive thyroid gland or aging has slowed the heart. In these situations, taking medication or having a pacemaker implanted may be needed.

Bradycardia can also occur because of a nutritional imbalance. If this is the cause, your doctor may recommend a dietary supplement. In addition, the condition can be a side effect of medication, and in those cases a doctor may adjust your prescription.

6. Long QT Syndrome

A number of other disorders occur because of problems with the heart's electrical system. Long QT syndrome, a hereditary disorder that usually affects children or young adults, slows the signal that causes the ventricles to contract. Another electrical signal problem, atrial flutter, happens when a single electrical wave circulates rapidly in the atrium, causing a very fast but steady heartbeat. Heart block involves weak or improperly conducted electrical signals from the upper chambers that can't make it to the lower chambers, causing the heart to beat too slowly. These conditions can put you at risk for cardiac arrest. Treatment might involve medication, ablation, or an implanted device to correct the misfiring, such as a pacemaker or defibrillator.